First, it's important to know that those in the Churches of Christ have made an understandable but false assumption that to be saved, what a person needs to do is read the Bible, believe it, and then cooperate with all the "right" or necessary moral and religious commands or requirements as they are found in the New Testament.
These moral and religious commands include hearing, believing, repenting of sin, confessing the name of Christ, and being water baptized, and then trying to live and worship correctly, being faithful unto death.
Here, humanly speaking, the Churches of Christ make an understandable assumption.
However biblically speaking, keep in mind this isn't the gospel of Jesus Christ (1 Cor. 15:1-11), nor does it take into account the dynamics of the fall and resulting sinfulness of man (Romans 5:12-21).
The Bible tells us that because of Adam's sin, man is a sinner and that even as believers we all sin and stumble in many ways. And because the 'wages of sin is death' and 'the soul that sins shall die', we can never go to heaven based upon our imperfect good works and why we are in such Great need of Savior.
The Gospel or GOOD NEWS Message is that as our substitute, Jesus went to the cross and took the FULL penalty for our sin- "the just for the unjust" and died in our place. Jesus also lived holy for us so that the basis of going to heaven is based on His perfect life and not our own. Jesus has become for us "our righteousness, holiness, and redemption" and is available to every person who places faith in Jesus Christ- 'to all and upon all who place faith in Jesus.' Romans 3:21-31; I Cor. 1:30
Please note, the real point of contention between evangelicals and the Churches of Christ is between 'works righteousness" (that righteousness that is attained by doing the right thing, the right way, for the right reason) and 'faith righteousness' (that righteousness which is a gift from God, brought to us by Christ, and received by faith).
Our point is that the righteousness that is by faith in Jesus Christ far supersedes works righteousness that is by someone 'doing the right thing, the right way, for the right reason', because the forgiveness and righteousness of Jesus is directly given, credited, or imputed unto the believer.
As Phil. 3:9 says, "... not having my own righteousness, which is of the law, but that (righteousness) which is through faith in Christ, the righteousness which is from God by faith."
The second item one should know is that when sharing the gospel with those in the Church of Christ and telling them of the righteousness that is given to us by faith, it's important to know that the Church of Christ concept of the doctrine justification by faith alone is flawed.
This is important.
You see, your belief that we are saved by placing faith in Jesus Christ is understood (and often falsely asserted) as though it teaches nothing more than salvation by merely believing "as true" the facts of the Christian faith. So when you tell them we are saved by placing faith in the Savior, what they hear is 'salvation by mere intellectual assent'.
And being well aware that even the demons "believe" and that just believing the facts of Christianity does not save, those in the Churches of Christ 'throw the baby out with the bath water' and thus rejects the entire doctrine of salvation by faith in Jesus Christ alone.
Therefore they embrace a mixed-up gospel theology of works and "water" baptism for salvation by default and seldom, if ever, come to a biblical understanding of how a person is saved by placing faith and trust in the Savior.
Our message to share is that justification by faith does not mean 'salvation by merely believing the facts of the Christian faith', but rather it is you believing God's promise that on the cross Jesus Christ took upon Himself ALL of God's wrath and anger for our sin, that God punished Jesus so that He wouldn't have to punish us, and that God raised Him from the dead. 1 Cor. 15:1-11
Please note, it's certainly possible to believe that someone is the president of the United States; However, just because you believe this to be factually true, doesn't necessarily mean or imply that you have faith in them as president.
Again, there is a radical difference between mere intellectual assent and faith, or in other words a difference between believing the historical fact that Jesus lived, died, and rose again, and believing God's promise that Jesus lived, died on the cross, and rose again for you.
Our Message to share
Now convincing them that that there is a difference between intellectual assent and faith in the person and work of Jesus Christ is only half our problem.
We still must be able to show where the doctrine of justification by faith is found in the Scripture.
Personally, as one who has grown up in the Churches of Christ, my first reaction after being introduced to this doctrine itself was, "That's interesting. I wonder where they (i.e. Baptists and other evangelicals) found this doctrine in Scripture?"
Though it may be hard to believe, I had simply never heard this doctrine before and I was curious to know how people could possibly come to such a conclusion based upon the Word of God.
It wasn't until later that I found out that there are 154 passages in the New Testament that tell us salvation is by placing our faith in Jesus Christ, that it is systematically taught in the book of Romans in chapters 1, 3, 4, 5, 9, 10 & 11, and because of a doctrinal controversy is also addressed in Galatians, chapters 2, 3, 4 & 5.
In other words, be sure to be able show where this doctrine is systematically taught and explained from the Word of God, and that it is not some abstract or obscure doctrine taken out of context from a few passages of scriptures- as it is often asserted.
What is important?
Now may I say that there will be a tremendous temptation to argue with the Church of Christ over some point of their doctrine, such as their belief system of "water" baptism for the forgiveness of sins.
Here we can agree that we are identified/ baptized into Christ when we are saved. However, let us be clear that what we are talking about is the true or actual baptism of Holy Spirit baptism, rather than the rite, ritual or "water" baptism, which is the believer's outward sign or symbol of that event.
In all four gospels John the Baptist said, 'I baptize you with (the medium of) water. But the One who comes after me He will baptize you with (the medium of) the Holy Spirit.'
Our point is, it is when we hear the gospel and believe it, placing our faith and trust in Jesus Christ, that God responds by giving us new birth through the baptism of the Holy Spirit that comes upon us at conversion-
“For by one Spirit we were all baptized into one body- whether Jews or Greeks, whether slave or free- and have all been made to drink into one Spirit.” 1 Cor. 12:13
Thus "water" baptism, which unfortunately is what the Church of Christ member is betting their entire eternal destiny upon (i.e. getting their outward flesh immersed in h2o) is the believer's sign or a symbol of the true or actual baptism of the Holy Spirit that occurs the moment the believer places their faith Jesus Christ.
Again, good works now evident in the life of the believer are not our own personal contribution to our own salvation, but is merely the result of our new life and new spiritual birth that occurs the moment a person places faith in Jesus.
Questions for Discussion and Witnessing
Finally, I would recommend starting any salvation conversation your Church of Christ friend simply by asking them two questions:
First, although they are convinced "faith alone" is a false doctrine, ask them what they believe the doctrine of justification by faith alone actually teaches. In other words, you are asking them to explain what they believe the doctrine of justification by faith alone actually teaches.
Rest assured they will give the Church of Christ narrative or that faith alone teaches 'a person can be saved simply by believing as true the facts of the Christian faith.'
Second, ask them- although they disagree with the doctrine (or rather their mis-understanding of the doctrine), where people are convinced the doctrine of justification by faith alone is taught and explained from the Word of God.
And here I will say they will have no idea.
Church of Christ members are experts at going from one pretext verse to another, from one chapter context to another, and from one book context to another, to "prove" what they already believe. So sitting down and reading "verse by verse" and "passage by passage" the great doctrinal books of the New Testament is often a complete mystery. To them the book of Romans was written with just 8 verses in chapter 6 and what they believe is being taught- water baptism for salvation. Galatians is viewed in very much the same way. While they are quite familiar with chapter one and 'if we or an angel from heaven preach any other gospel than what you have received, let him be accursed'- yet the great doctrine of justification by faith, which is the great theme of the book, is completely overlooked and missed.
Notice what Paul writes in Galatians 2:15-16:
"We who are Jews by nature, and not sinners of the Gentiles, knowing that a man is not justified by the works of the law but by faith in Jesus Christ, even we have believed in Christ Jesus, that we might be justified by faith in Christ and not by the works of the law; for by the works of the law no flesh shell be justified."
Anyway, asking these two questions can be helpful in accomplishing two things:
First, it may give you the opportunity to clarify both what the doctrine of justification by faith alone actually teaches (and what it doesn’t teach), and second, it may also give you the opportunity TO SHOW WHERE the doctrine is systematically found, taught, and explained from the Word of God.
Again, there are over 150 places in the New Testament that salvation is received by faith in Christ with nothing else added, and it is systematically taught and explained in the books of Romans and Ephesians.
Thus given this information, to accept or reject the gospel is now up to them. May God open their hearts to believe upon Jesus Christ and Him alone for eternal life.